CN107785920A - Ground return turns control method, device and the transmission system of metallic return - Google Patents
Ground return turns control method, device and the transmission system of metallic return Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
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Abstract
The embodiment provides control method, device and the transmission system that a kind of Ground return turns metallic return, it is related to power electronic equipment control technology field, MTDC transmission system is solved with the end number of current conversion station and the increase of transmission line of electricity, how safely and effectively to cause MTDC transmission system Ground return turns metallic return the problem of.This method includes, collection flow through each current conversion station Ground return electric current as the electric current of the first measurement data and the metallic return for flowing through each current conversion station as the second measurement data；According to the first measurement data and the second measurement data, it is determined that each current conversion station is converted to the operation order of metallic return by Ground return；According to operation order, the Ground return of each current conversion station is converted into metallic return.The embodiment of the present invention is used for the control that Ground return turns metallic return.
Description
Technical Field
The invention relates to the technical field of power electronic device control, in particular to a method and a device for controlling a ground return wire to a metal return wire and a power transmission system.
Background
High voltage direct current transmission has several modes of operation, with the transition between earth return and metallic return being a very common operation. Generally, a high-voltage direct-current system is in a bipolar operation mode, when one pole needs to be quitted from shutdown due to some reason, the high-voltage direct-current system is switched from the bipolar operation to the monopolar ground loop operation, a large amount of injection current flows to the ground through a grounding pole, and a main transformer near the grounding pole is likely to be subjected to direct-current magnetic biasing and influence on the ecological environment near the grounding pole.
In order to avoid the negative effects of the ground current, it is common to return the hvdc system from the unipolar ground return to the metallic return using the first pole line (which for some reason needs to be taken out of service) as the return path for the current. Because frequent shutdown of the high-voltage direct-current system can generate large impact on alternating-current systems on two sides, in order to improve the reliability and the availability of the operation of the high-voltage direct-current system, the ground return wire and the metal return wire are generally required to be carried out under the condition that the system is not in shutdown when being switched with each other.
For a two-terminal system, because only one line exists, according to the shunt principle, when a metal Return line and a Ground Return line are operated in parallel, the ratio of the current passing through a Metal Return Transfer Breaker (MRTB) to the current passing through a Ground Return Transfer Switch (GRTS) is inversely proportional to the ratio of the Ground Return line resistance to the metal Return line resistance. Usually, the resistance of the metal return line in the direct current engineering is greater than that of the ground return line, so when the ground return line and the metal return line coexist, the current flowing through the MRTB is greater than the current of the GRTS; in the process of load operation, the MRTB operation condition is worse than the GRTS operation condition.
Because of this, according to the operation experience of the domestic existing engineering, the case that the ground return wire is converted into the metal return wire is more than that the metal return wire is converted into the ground return wire. How to safely and effectively convert a multi-terminal direct current system into a metal return wire on an earth return wire becomes a problem to be solved urgently along with the increase of the end number of a converter station and the increase of a power transmission line of the multi-terminal direct current system.
Disclosure of Invention
The embodiment of the invention provides a method and a device for controlling a ground return wire to be converted into a metal return wire and a power transmission system, and solves the problem of how to safely and effectively convert a multi-terminal direct current system into the metal return wire from the ground return wire along with the increase of the number of terminals of a converter station and the increase of a power transmission line.
In order to achieve the above purpose, the embodiment of the invention adopts the following technical scheme:
in a first aspect, an embodiment of the present invention provides a method for controlling a ground return wire to a metal return wire, which is applied to a multi-terminal dc system, where the multi-terminal dc system includes three or more converter stations, and includes: collecting current flowing through the earth return wire of each converter station as first measurement data and current flowing through the metal return wire of each converter station as second measurement data; determining an operation sequence of converting the earth return wire into the metal return wire of each converter station according to the first measurement data and the second measurement data; the earth return of each converter station is converted to a metallic return according to the operating sequence.
Optionally, the determining, according to the first measurement data and the second measurement data, an operation sequence for converting the earth return wire into the metallic return wire for each converter station includes: calculating the current flowing through the earth return wire and the metal return wire of each converter station when the earth return wire and the metal return wire of each converter station exist at the same time according to the first measurement data and the second measurement data; the sequence of operations for each converter station to convert from earth return to metallic return is determined from the current of the earth return and the current of the metallic return of the converter station.
Optionally, the multi-terminal dc transmission system includes a rectification station, a first inverter station, and a second inverter station; the first measurement data comprises the actual current of the earth return line; the second measurement data comprises the actual current of the metallic return wire; determining the sequence of operations for each converter station to convert from earth return to metallic return from the first measurement data and the second measurement data comprises: when the first measurement data and the second measurement data satisfy the following inequality set,
the operation sequence comprises the following steps: the sequence of the rectification station, the first inversion station and the second inversion station; wherein R1 represents the equivalent resistance of the grounding electrode of the rectifier station, R2 represents the equivalent resistance of the grounding electrode of the first inverter station, R3 represents the equivalent resistance of the grounding electrode of the second inverter station, RL1 represents the equivalent resistance of the line between the rectifier station and the first inverter station, RL2 represents the equivalent resistance of the line between the first inverter station and the second inverter station,representing the rated dc current of the first inverter station,representing the rated dc current of the second inverter station.
Optionally, the multi-terminal dc power transmission system includes a rectifying station, a first inverter station, and a second inverter station; the first measurement data comprises the actual current of the earth return line; the second measurement data comprises the actual current of the metallic return wire; according to the first measurement data and the second measurement data, the operation sequence of converting the rectifying station and each inversion station from the earth return wire to the metal return wire comprises the following steps: when the first measurement data and the second measurement data satisfy the following inequality set,
the operation sequence comprises: the sequence of the rectification station, the first inversion station and the second inversion station; wherein R1 represents the equivalent resistance of the grounding electrode of the rectifier station, R2 represents the equivalent resistance of the grounding electrode of the first inverter station, R3 represents the equivalent resistance of the grounding electrode of the second inverter station, RL1 represents the equivalent resistance of the line between the rectifier station and the first inverter station, RL2 represents the equivalent resistance of the line between the first inverter station and the second inverter station,representing the rated dc current of the first inverter station,representing the rated dc current of the second inverter station.
In a second aspect, an embodiment of the present invention provides a control apparatus for converting a ground return wire into a metal return wire, which is applied to a multi-terminal dc system, where the multi-terminal dc system includes three or more converter stations, and the control apparatus includes: the data acquisition unit is used for acquiring current flowing through the earth return wire of each converter station as first measurement data and current flowing through the metal return wire of each converter station as second measurement data; the data processing unit is used for determining the operation sequence of converting the earth return wire into the metal return wire of each converter station according to the first measurement data acquired by the data acquisition unit and the second measurement data acquired by the data acquisition unit; and the data processing unit is also used for converting the earth return wire of each converter station into a metal return wire according to the operation sequence.
Optionally, the data processing unit is further configured to calculate, according to the first measurement data acquired by the data acquisition unit and the second measurement data acquired by the data acquisition unit, currents flowing through the ground return wire and the metal return wire of the inverter station when the ground return wire and the metal return wire of each inverter station exist at the same time; and the data processing unit is also used for determining the operation sequence of converting the earth return wire into the metal return wire of each converter station according to the current of the earth return wire of the converter station and the current of the metal return wire of the converter station.
Optionally, the multi-terminal dc transmission system includes a rectification station, a first inverter station, and a second inverter station; the first measurement data comprises the actual current of the earth return line; the second measurement data comprises the actual current of the metal return wire; a data processing unit, which is used for acquiring the first measurement data and the second measurement data when the first measurement data and the second measurement data satisfy the following inequality set,
the operation sequence comprises: the sequence of the rectifier station, the first inverter station and the second inverter station; wherein R1 represents the equivalent resistance of the grounding electrode of the rectifier station, R2 represents the equivalent resistance of the grounding electrode of the first inverter station, R3 represents the equivalent resistance of the grounding electrode of the second inverter station, RL1 represents the equivalent resistance of the line between the rectifier station and the first inverter station, RL2 represents the equivalent resistance of the line between the first inverter station and the second inverter station,representing the rated dc current of the first inverter station,representing the rated dc current of the second inverter station.
Optionally, the multi-terminal dc power transmission system includes a rectifying station, a first inverter station, and a second inverter station; the first measurement data comprises the actual current of the earth return line; the second measurement data comprises the actual current of the metallic return wire; a data processing unit, which is used for acquiring the first measurement data and the second measurement data when the first measurement data and the second measurement data satisfy the following inequality set,
the operation sequence comprises: the sequence of the rectification station, the first inversion station and the second inversion station; wherein R1 represents the equivalent resistance of the grounding electrode of the rectifier station, R2 represents the equivalent resistance of the grounding electrode of the first inverter station, R3 represents the equivalent resistance of the grounding electrode of the second inverter station, RL1 represents the equivalent resistance of the line between the rectifier station and the first inverter station, RL2 represents the equivalent resistance of the line between the first inverter station and the second inverter station,representing the rated dc current of the first inverter station,representing the rated dc current of the second inverter station.
In a third aspect, embodiments of the invention provide a power transmission system comprising any one of the earth return to metal return control apparatus as provided in the second aspect.
According to the control method, device and power transmission system for converting the ground return wire into the metal return wire, which are provided by the embodiment of the invention, the current flowing through the ground return wire of each converter station is acquired as first measurement data, and the current flowing through the metal return wire of each converter station is acquired as second measurement data; determining the operation sequence of each converter station for converting the earth return wire into the metal return wire according to the first measurement data and the second measurement data; converting the earth return wire of each converter station into a metallic return wire according to the operation sequence; the method and the device ensure that the ground return wire is converted into the metal return wire safely and effectively by the multi-terminal direct current system, thereby solving the problem of how to safely and effectively convert the multi-terminal direct current system into the metal return wire on the ground return wire along with the increase of the number of the terminals of the converter station and the increase of the transmission line.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic flowchart of a method for controlling a ground return to a metallic return according to an embodiment of the present invention;
fig. 2 is an applicable circuit structure of a method for controlling a ground return to a metal return according to an embodiment of the present invention;
3-a-3-d are test data charts of a method for controlling a ground return to a metal return according to an embodiment of the present invention in practical application;
fig. 4 is a schematic structural diagram of a control device for converting a ground return wire into a metal return wire according to an embodiment of the present invention.
Reference numerals:
a control device-10 for converting the ground return wire into the metal return wire;
a data acquisition unit-101;
a data processing unit-102.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
A first embodiment and an embodiment of the present invention provide a method for controlling a ground return to a metallic return, which is applied to a multi-terminal dc system, where the multi-terminal dc system includes three or more converter stations, and as shown in fig. 1, the method includes:
s101, collecting current flowing through the earth return wire of each converter station as first measurement data and current flowing through the metal return wire of each converter station as second measurement data.
It should be noted that the initial operating state of the multi-terminal direct-current power transmission system is a single-pole ground loop operation; plural means greater than or equal to three; the rectifying station, the first inverter station and the second inverter station each comprise a first pole and a second pole as shown in fig. 1, where the first pole and the second pole are two poles located opposite in polarity; for example, assuming that the second poles of the rectifier station and the inverter station stop operating due to a fault or maintenance, the lines of the first poles of the three converter stations are connected with the ground to form a ground loop; at this time, the second pole is already out of operation, but the line of the second pole still exists, and the line of the second pole can be used as a return line, so that a metal loop is formed; in practical applications, as shown in fig. 2, data required for conversion between two operation modes (ground return and metal return) need to be collected and measured, including an actual current IS1_ M of the metal return of the rectifier station, an actual current IS2_ M of the metal return of the first inverter station, an actual current IS3_ M of the metal return of the second inverter station and a current IS1_ G of the ground return of the rectifier station, a current IS2_ G of the ground return of the first inverter station, and a current IS3_ G of the ground return of the second inverter station.
And S102, determining the operation sequence of converting the earth return wire into the metal return wire of each converter station according to the first measurement data and the second measurement data.
It should be noted that, in practical applications, since the ground return line cannot be switched to the metallic return line in a moment, the current multi-terminal dc system needs to be analyzed, so as to determine how to finally convert the ground return line to the metallic return line;
step 1, firstly, earth metal return line conversion is completed on the rectifying station S1 and the first inverter station S2, and then earth metal return line conversion of the second inverter station S3 is completed (the earth metal return line conversion means that earth return lines are converted into metal return lines).
And 2, completing earth metal return line conversion for the S1 and the S3, and then completing earth metal return line conversion for the S2.
Wherein, the operation sequence in the step 1 has the following intermediate conversion state that the earth metal return wires coexist; specifically, the whole process of the earth metal return wire conversion in the step 1 is as follows:
an initial state: and S1, S2 and S3, running the ground loop.
Intermediate state 1: s1, the earth metal return wires coexist; s2, the earth metal return wires coexist; s3, returning the ground.
Intermediate state 2: s1, the earth metal return wires coexist; s2, a metal loop is formed; s3, returning the ground.
Intermediate state 3: s1, the earth metal return wires coexist; s2, a metal loop is formed; s3, the earth metal loops coexist.
And (3) final state: s1, a metal loop is formed; s2, a metal return wire; and S3, a metal loop.
Wherein, the operation sequence in the step 2 has the following intermediate conversion states in which the earth metal return wires coexist; specifically, the whole process of ground metal loop conversion in the step 2 is as follows:
an initial state: and S1, S2 and S3 are operated by ground return wires.
Intermediate state 1: s1, the earth metal return wires coexist; s2, returning the earth; s3, the earth metal loops coexist.
Intermediate state 2: s1, the earth metal return wires coexist; s2, returning the earth; and S3, a metal loop.
Intermediate state 3: s1, the earth metal return wire 2 coexists; s2, the earth metal return wires coexist; s3, a metal loop is formed.
And (3) final state: s1, a metal loop is formed; s2, a metal loop is formed; s3, a metal loop is formed.
And S103, converting the earth return wire of each converter station into a metal return wire according to the operation sequence.
Optionally, the determining, according to the first measurement data and the second measurement data, an operation sequence for converting the earth return wire into the metallic return wire for each converter station includes: calculating the current flowing through the ground return wire and the metal return wire of each converter station when the ground return wire and the metal return wire of each converter station exist at the same time according to the first measurement data and the second measurement data; the sequence of operations for each converter station to convert from earth return to metallic return is determined from the current of the earth return and the current of the metallic return of the converter station.
Optionally, the multi-terminal dc power transmission system includes a rectifying station, a first inverter station, and a second inverter station; the first measurement data comprises the actual current of the earth return line; the second measurement data comprises the actual current of the metal return wire; determining the sequence of operations for converting each station from earth return to metallic return from the first measurement data and the second measurement data comprises: when the first measurement data and the second measurement data satisfy the following inequality set,
the operation sequence comprises: the sequence of the rectification station, the first inversion station and the second inversion station; wherein R1 represents the equivalent resistance of the grounding electrode of the rectifier station, R2 represents the equivalent resistance of the grounding electrode of the first inverter station, R3 represents the equivalent resistance of the grounding electrode of the second inverter station, RL1 represents the equivalent resistance of the line between the rectifier station and the first inverter station, RL2 represents the equivalent resistance of the line between the first inverter station and the second inverter station,representing the rated dc current of the first inverter station,representing the rated dc current of the second inverter station.
In the case of ground-to-ground metal interconversion, the ground return and metallic return currents in the respective intermediate states in the presence of the ground return and the metallic return need to be estimated in advance based on the first measurement data before the conversion as follows:
under the condition that the ground metal loops S1 and S3 coexist in the intermediate state, the currents of the ground metal loops and the metal loops passing through S3 are respectively as follows:
for the condition that the earth metal return wires in the intermediate state S1 coexist, the earth metal return wires in the intermediate state S2 coexist, and the earth return wires and the metal return wires passing through the intermediate state S2 respectively have the following currents:
when the operation mode of the ground to the metal return wire is switched, in order to ensure the safety and the reliability of the grounding electrode, the current passing through the grounding electrode and the metal return wire is smaller than the rated current of the station, namely:
when the operation of step 1 is carried out, the conditions are satisfied
Since the main circuit parameters cannot be changed, the currents of the earth and the metal return do not exceed the rated values of the stationsTherefore, the number of the first and second electrodes is increased,
in the operation of step 1, before the ground return operation, the dc current flowing through S2 and the dc current flowing through S3 should satisfy inequalities (5) to (8).
In general, the resistance of the grounding electrode is smaller than that of the metal loop, namely R1 is smaller than RL1, R1 is smaller than RL2, R2 is smaller than RL1, R2 is smaller than RL2, R3 is smaller than RL1, and R3 is smaller than RL2.
For two inverter stations with different power levels, when IS2_ G < IS3_ G, the sequence of step 1 IS proposed, i.e. the earth metal conversion of S2 IS performed first, the earth metal conversion process of S3 IS performed after S2 IS completely converted into the earth return wire, and the earth metal conversion process of S1 IS performed after S3 IS completely converted into the earth return wire until S1 IS completely converted into the earth return wire.
Optionally, the multi-terminal dc transmission system includes a rectification station, a first inverter station, and a second inverter station; the first measurement data comprises the actual current of the earth return line; the second measurement data comprises the actual current of the metal return wire; according to the first measurement data and the second measurement data, the operation sequence of converting the earth return wire into the metal return wire of the rectifying station and each inversion station comprises the following steps: when the first measurement data and the second measurement data satisfy the following inequality set,
the operation sequence comprises: the sequence of the rectification station, the first inversion station and the second inversion station; wherein R1 represents the equivalent resistance of the grounding electrode of the rectifier station, R2 represents the equivalent resistance of the grounding electrode of the first inverter station, R3 represents the equivalent resistance of the grounding electrode of the second inverter station, RL1 represents the equivalent resistance of the line between the rectifier station and the first inverter station, RL2 represents the equivalent resistance of the line between the first inverter station and the second inverter station,representing the rated dc current of the first inverter station,representing the rated dc current of the second inverter station.
In the case of ground-to-ground metal interconversion, the ground return and metallic return currents in the respective intermediate states in the presence of the ground return and the metallic return need to be estimated in advance based on the first measurement data before the conversion as follows:
for the situation that the earth metal return wires coexist in the intermediate state S1, the earth metal return wires coexist in the intermediate state S2, and the earth metal return wires coexist in the intermediate state S3, the earth return wire and the metal return wire currents passing through the intermediate state S3 are respectively as follows:
for the condition that the earth metal return wires in the intermediate state S1 coexist, the earth metal return wires in the intermediate state S2 coexist, and the earth metal return wires and the metal return wires passing through the intermediate state S2 respectively have the following currents:
when the ground-to-metal loop operation mode is switched, in order to ensure the safety and reliability of the grounding electrode, the current passing through the grounding electrode and the metal loop should be smaller than the rated current of the station, namely:
when the step 2 operation is carried out, the conditions are satisfied
Since the main circuit parameters cannot be changed, the currents of the earth and the metal return do not exceed the rated values of the stationsTherefore, the temperature of the molten metal is controlled,
in the operation of step 2, before the ground return operation, the dc current flowing through S2 and the dc current flowing through S3 should satisfy the inequality groups (13) to (16).
In general, the resistance of the grounding electrode is smaller than that of the metal loop, namely R1 is smaller than RL1, R1 is smaller than RL2, R2 is smaller than RL1, R2 is smaller than RL2, R3 is smaller than RL1, and R3 is smaller than RL2.
Therefore, for two inverter stations with different power levels, when IS2_ G > IS3_ G, it IS proposed to operate in the order of step 2, i.e. perform the earth-metal conversion of S3 first, perform the earth-metal conversion process of S2 after S3 IS completely converted into the earth return line, and perform the earth-metal conversion process of S1 after S2 IS completely converted into the earth return line until S1 IS completely converted into the earth return line.
When the current IS2_ G flowing through the earth return line of the first inverter station and the current IS3_ G flowing through the earth return line of the second inverter station do not satisfy neither the inequality groups (5) - (8) nor the inequality groups (13) - (16), the operation condition before the earth metal conversion needs to be adjusted, so that the direct current flowing through S2 and the direct current flowing through S3 satisfy the inequality groups (5) - (8) or the inequality groups (13) - (16) before the earth-turning metal return line operation IS performed.
Specifically, in order to clearly show the method for controlling a ground return wire to a metal return wire provided by the embodiment of the present invention, the present invention is further described in detail in practical application with reference to fig. 1, and the specific implementation manner is as follows:
the overall process of the pole 1 being converted from earth return to metallic return operation will now be briefly described, taking as an example the wiring diagram of the three-terminal dc transmission system shown in fig. 1. Figure 1 shows only switches, disconnectors, circuit breakers etc. that are involved in earth return conversion. Fig. 1 includes 3 converter stations, the rectifier station S1 is a converter station based on LCC, and the inverter station S2 and the inverter station S3 are converter stations based on MMC. The rated direct current voltage level of power transmission is 800kV, and the rated power of the three convertor stations is 8000MW, 3000MW and 5000MW respectively. The two inversion stations are respectively provided with a ground return line change-over switch GRTS and a metal return line change-over switch MRTB. The equivalent line resistance between S1 and S2 is 3.75 Ω, and the equivalent line resistance between S2 and S3 is 3.63 Ω. The equivalent resistances of the three-station grounding electrode circuit and the grounding electrode are 0.4 omega, 2.4 omega and 1.7 omega. When the three stations operate, the rectifying station S1 and the inverter station S2 are controlled by constant current, and the inverter station S3 is controlled by constant voltage.
The initial state of the system is that the poles 1 of S1, S2 and S3 are operated in the operating state of the monopole earth return wire, and the poles 2 of the three converter stations are all in the off-operating state. The bypass buses of the three stations are not put into use, all NBS switches are in an open state, MRTB of the two inverter stations are in a closed state, and GRTS is in an open state.
Since the initial state of the system is that the pole 1 is in the rated operation state, before the ground-to-ground metal return operation is performed, the dc current flowing through S2 and the dc current flowing through S3 should satisfy the inequality groups (5) - (8), according to the above technical solution, the conversion process is performed according to the operation sequence of step 1, and the specific operation is as follows:
1. the system is in an initial state of three-station monopole ground loop operation, and after the system receives a metal loop operation command to be performed, the following switches NBS _ S1_ P2 and NBS _ S2_ P2 are respectively closed when t =3S, and GRTS _ S2 forms a metal loop circuit between S1 and S2;
2. after Im _ S2 and Ig _ S2 are stabilized, disconnecting MRTB _ S2 when t =5S, and completing the conversion process of the earth return wire to the metal return wire by S2;
3. NBS _ S3_ P2 is closed at t =6S, GRTS _ S3 forming a metallic return loop between S1 and S3, respectively;
4. and when t =8S, after Im _ S3 and Ig _ S3 are stabilized, MRTB _ S3 is disconnected, and S3 completes the conversion process of the earth return wire to the metallic return wire.
The simulation result of the current on the three-station ground metal return wire in the whole process is shown in fig. 3-a (fig. 3-a shows the current on the three-station ground metal return wire and the ground return wire when the operation is performed according to the step 1 in the rated state).
When the operation is performed according to the operation sequence of step 2, the specific operations are as follows:
1. the system is in an initial state of three-station monopole ground loop operation, and after the system receives a metal loop operation command to be performed, the following switches NBS _ S1_ P2 and NBS _ S3_ P2 are respectively closed when t =3S, and GRTS _ S3 forms a metal loop circuit between S1 and S3;
2. when t =5S, after Im _ S3 and Ig _ S3 are stabilized, MRTB _ S3 is disconnected, and S3 completes the conversion process of the earth return wire to the metallic return wire;
3. t =6S followed by respectively closing NBS _ S2_ P2, GRTS _ S2 forming a metallic loop between S1 and S2;
4. and when t =8S, after Im _ S2 and Ig _ S2 are stabilized, MRTB _ S3 is disconnected, and S3 completes the conversion process of the earth return wire to the metallic return wire.
The simulation result of the current on the three-station ground metal return wire in the whole process is shown in fig. 3-b (fig. 3-b shows the current on the three-station ground metal return wire and the ground return wire when the operation is carried out according to the step 2 under the rated state). According to simulation results of fig. 3-c (fig. 3-c shows the current on the earth return wire when the earth return wires of S3 stations coexist in step 2 in the rated state) and fig. 3-d (fig. 3-d shows the current on the earth return wire when the earth return wires of S3 stations coexist in step 1 in the rated state), S2 bears the earth current 1.5 times of the rated current when the earth return wires coexist, which greatly affects the safe and reliable operation of the earth electrode; therefore, it is more reasonable to select the operation sequence of step 1.
The control method for converting the earth return wire into the metal return wire provided by the embodiment of the invention collects the current of the earth return wire flowing through each converter station as first measurement data and the current of the metal return wire flowing through each converter station as second measurement data; thereby determining the operation sequence of converting the earth return wire into the metal return wire of each converter station according to the first measurement data and the second measurement data; converting the earth return wire of each converter station into a metallic return wire according to the operation sequence; the method and the device ensure that the ground return wire is converted into the metal return wire safely and effectively by the multi-terminal direct current system, thereby solving the problem of how to safely and effectively convert the multi-terminal direct current system into the metal return wire on the ground return wire along with the increase of the number of the terminals of the converter station and the increase of the transmission line.
A second embodiment of the present invention provides a control apparatus for converting a ground return wire into a metallic return wire, which is applied to a multi-terminal dc system, where the multi-terminal dc system includes three or more converter stations, as shown in fig. 4, including:
a data acquisition unit 101 is configured to acquire a current flowing through the earth return of each converter station as first measurement data and a current flowing through the metal return of each converter station as second measurement data.
And the data processing unit 102 is configured to determine an operation sequence of each converter station for converting the earth return wire into the metal return wire according to the first measurement data acquired by the data acquisition unit 101 and the second measurement data acquired by the data acquisition unit 101.
The data processing unit 102 is further adapted to convert the earth return of each converter station into a metallic return according to the operation sequence.
Optionally, the data processing unit 102 is further configured to calculate, according to the first measurement data obtained by the data obtaining unit 101 and the second measurement data obtained by the data obtaining unit 101, currents flowing through the ground return wire and the metallic return wire of the inverter station when the ground return wire and the metallic return wire of each converter station exist at the same time; the data processing unit 102 is further configured to determine an operation sequence for each converter station to convert the earth return wire into the metal return wire according to the current of the earth return wire of the converter station and the current of the metal return wire of the inverter station.
Optionally, the multi-terminal dc transmission system includes a rectification station, a first inverter station, and a second inverter station; the first measurement data comprises the actual current of the earth return line; the second measurement data comprises the actual current of the metal return wire; a data processing unit 102, specifically configured to, when the first measurement data acquired by the data acquisition unit 101 and the second measurement data acquired by the data acquisition unit 101 satisfy the following inequality set,
the operation sequence comprises: the sequence of the rectifier station, the first inverter station and the second inverter station; wherein R1 represents the equivalent resistance of the grounding electrode of the rectifier station, R2 represents the equivalent resistance of the grounding electrode of the first inverter station, R3 represents the equivalent resistance of the grounding electrode of the second inverter station, RL1 represents the equivalent resistance of the line between the rectifier station and the first inverter station, RL2 represents the equivalent resistance of the line between the first inverter station and the second inverter station,representing the rated dc current of the first inverter station,representing the rated dc current of the second inverter station.
Optionally, the multi-terminal dc transmission system includes a rectification station, a first inverter station, and a second inverter station; the first measurement data comprises the actual current of the earth return line; the second measurement data comprises the actual current of the metal return wire; a data processing unit 102, specifically configured to, when the first measurement data acquired by the data acquisition unit 101 and the second measurement data acquired by the data acquisition unit 101 satisfy the following inequality set,
the operation sequence comprises: the sequence of the rectification station, the first inversion station and the second inversion station; wherein R1 represents the equivalent resistance of the grounding electrode of the rectifier station, R2 represents the equivalent resistance of the grounding electrode of the first inverter station, R3 represents the equivalent resistance of the grounding electrode of the second inverter station, RL1 represents the equivalent resistance of the line between the rectifier station and the first inverter station, RL2 represents the equivalent resistance of the line between the first inverter station and the second inverter station,representing the rated dc current of the first inverter station,representing the rated dc current of the second inverter station.
The control device for converting the earth return wire into the metal return wire provided by the embodiment of the invention collects the current of the earth return wire flowing through each converter station as first measurement data and the current of the metal return wire flowing through each converter station as second measurement data; determining the operation sequence of each converter station for converting the earth return wire into the metal return wire according to the first measurement data and the second measurement data; converting the earth return wire of each converter station into a metallic return wire according to the operation sequence; the method and the device ensure that the ground return wire is converted into the metal return wire safely and effectively by the multi-terminal direct current system, thereby solving the problem of how to safely and effectively convert the multi-terminal direct current system into the metal return wire from the ground return wire along with the increase of the number of the terminals of the converter station and the increase of the transmission line.
Embodiment three, an embodiment of the present invention provides a power transmission system, comprising any one of the earth return to metal return control apparatus as provided in the second aspect.
According to the power transmission system provided by the embodiment of the invention, the current flowing through the earth return wire of each converter station is collected to serve as first measurement data, and the current flowing through the metal return wire of each converter station is collected to serve as second measurement data; thereby determining the operation sequence of converting the earth return wire into the metal return wire of each converter station according to the first measurement data and the second measurement data; converting the earth return wire of each converter station into a metallic return wire according to the operation sequence; the method and the device ensure that the ground return wire is converted into the metal return wire safely and effectively by the multi-terminal direct current system, thereby solving the problem of how to safely and effectively convert the multi-terminal direct current system into the metal return wire from the ground return wire along with the increase of the number of the terminals of the converter station and the increase of the transmission line.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.
Claims (9)
1. A control method for converting a ground return wire into a metal return wire is applied to a multi-terminal direct current system, wherein the multi-terminal direct current system comprises three or more converter stations, and the control method is characterized by comprising the following steps of:
collecting current flowing through the earth return wire of each converter station as first measurement data and current flowing through the metal return wire of each converter station as second measurement data;
determining an operation sequence of converting the earth return wire into the metal return wire of each converter station according to the first measurement data and the second measurement data;
and converting the earth return wire of each converter station into a metallic return wire according to the operation sequence.
2. The method of claim 1, wherein said determining the sequence of operations for converting the earth return to the metallic return for each of said converter stations from the earth return based on said first and second measurements comprises:
calculating the current flowing through the earth return wire and the metal return wire of each converter station when the earth return wire and the metal return wire of each converter station exist at the same time according to the first measurement data and the second measurement data;
and determining the operation sequence of converting the earth return wire into the metallic return wire of each converter station according to the current of the earth return wire of the converter station and the current of the metallic return wire of the converter station.
3. The method of claim 1, wherein said multi-terminal dc power transmission system comprises a rectifying station, a first inverter station and a second inverter station;
the first measurement data comprises an actual current of the earth return line; the second measurement data comprises the actual current of the metal return wire;
said determining, from said first and second measurements, an operational sequence for converting each of said converter stations from earth return to metallic return comprises:
when the first measurement data and the second measurement data satisfy the following inequality set,
the sequence of operations includes: the order of the rectifier station, the first inverter station and the second inverter station; wherein R1 represents an earth electrode equivalent resistance of the rectifier station, R2 represents an earth electrode equivalent resistance of the first inverter station, R3 represents an earth electrode equivalent resistance of the second inverter station, RL1 represents a line equivalent resistance between the rectifier station and the first inverter station, RL2 represents a line equivalent resistance between the first inverter station and the second inverter station,representing the rated dc current of the first inverter station,representing the rated dc current of the second inverter station.
4. A ground return to metal return control method according to claim 1 wherein said multi-terminal dc transmission system comprises a rectifier station, a first inverter station and a second inverter station;
the first measurement data comprises an actual current of the earth return line; the second measurement data comprises the actual current of the metal return wire;
the determining, according to the first measurement data and the second measurement data, an operation sequence of converting the rectifying station and each of the inverting stations from an earth return line to a metal return line includes:
when the first measurement data and the second measurement data satisfy the following inequality set,
the sequence of operations includes: the sequence of the rectifier station, the first inverter station and the second inverter station; wherein R1 represents an earth electrode equivalent resistance of the rectifier station, R2 represents an earth electrode equivalent resistance of the first inverter station, R3 represents an earth electrode equivalent resistance of the second inverter station, RL1 represents a line equivalent resistance between the rectifier station and the first inverter station, RL2 represents a line equivalent resistance between the first inverter station and the second inverter station,representing the rated dc current of the first inverter station,representing the rated dc current of the second inverter station.
5. A control device for converting a ground return wire into a metal return wire is applied to a multi-terminal direct current system, wherein the multi-terminal direct current system comprises three or more converter stations, and the control device is characterized by comprising:
the data acquisition unit is used for acquiring current flowing through the earth return wire of each converter station as first measurement data and current flowing through the metal return wire of each converter station as second measurement data;
the data processing unit is used for determining the operation sequence of converting each converter station from a ground return wire into a metal return wire according to the first measurement data acquired by the data acquisition unit and the second measurement data acquired by the data acquisition unit;
the data processing unit is further configured to convert the earth return of each converter station into a metallic return according to the operation sequence.
6. The apparatus for controlling earth return to metal return according to claim 5, wherein said data processing unit is further configured to calculate the current flowing through the earth return and the metal return of each converter station when the earth return and the metal return of each converter station exist simultaneously according to said first measurement data acquired by said data acquiring unit and said second measurement data acquired by said data acquiring unit;
the data processing unit is further configured to determine, according to the current of the earth return of the converter station and the current of the metallic return of the converter station, an operation sequence of converting the earth return into the metallic return of each converter station.
7. The apparatus for controlling a ground return to metal return of claim 5, wherein said multi-terminal DC power transmission system comprises a rectifying station, a first inverter station and a second inverter station;
the first measurement data comprises an actual current of the earth return line; the second measurement data comprises the actual current of the metal return wire;
the data processing unit is specifically configured to, when the first measurement data acquired by the data acquisition unit and the second measurement data acquired by the data acquisition unit satisfy the following inequality set,
the sequence of operations includes: the sequence of the rectifier station, the first inverter station and the second inverter station; wherein R1 represents an earth electrode equivalent resistance of the rectifier station, R2 represents an earth electrode equivalent resistance of the first inverter station, R3 represents an earth electrode equivalent resistance of the second inverter station, RL1 represents a line equivalent resistance between the rectifier station and the first inverter station, RL2 represents a line equivalent resistance between the first inverter station and the second inverter station,representing the rated dc current of the first inverter station,representing the rated dc current of the second inverter station.
8. An earth return to metal return control apparatus as claimed in claim 5 wherein said multi-terminal dc transmission system comprises a rectifier station, a first inverter station and a second inverter station;
the first measurement data comprises an actual current of the earth return line; the second measurement data comprises the actual current of the metal return wire;
the data processing unit is specifically configured to, when the first measurement data acquired by the data acquisition unit and the second measurement data acquired by the data acquisition unit satisfy the following inequality set,
the sequence of operations includes: the sequence of the rectifier station, the first inverter station and the second inverter station; wherein R1 represents an equivalent resistance of an earth electrode of the rectifier station, R2 represents an equivalent resistance of an earth electrode of the first inverter station, R3 represents an equivalent resistance of an earth electrode of the second inverter station, RL1 represents an equivalent resistance of a line between the rectifier station and the first inverter station,representing the rated dc current of the first inverter station,representing the rated dc current of the second inverter station.
9. A power transmission system comprising earth return to metal return control apparatus as claimed in any one of claims 5 to 8.
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